The preparation of hydroxamated acrylamide polymers is well known in the art. The hydroxamated polymers are disclosed as useful as chelating agents which are useful in the formation of iron complexes and are known to have a favorable effect on drilling muds. The use of these hydroxamated polymers as flocculants is also known.
U.S. Pat. No. 4,587,306 (L. Vio and G. Meunier, assigned to Societe Nationale Elf Aquitaine, 5/6/1986) teaches that hydroxamated polyacrylamides may be produced by the reaction of hydroxylamine with polyacrylamide in an aqueous solution at a temperature of 50.degree. to 85.degree. C. and a pH of about 6.2 to 6.8. The patent indicates that this temperature range is the optimum to minimize the decomposition of hydroxylamine while maintaining a reasonable reaction rate. The pH range disclosed is stated to be that which results in fast kinetics for the reaction. The polymers used were in the molecular weight range of 1000 to 20,000. Other references to making hydroxamated polyacrylamides include U.S. Pat. No. 3,345,344, which describes the reaction of hydroxylamine with a polyacrylonitrile followed by acid hydrolysis. French patent 2,476,113 discusses the reaction of hydroxylamine with polyacrylamide at 90.degree. C. using sodium acetate as a buffer. U.K. Published Patent Application 2171127 and U.S. Pat. Nos. 4,480,067; 4,532,046 and 4,536,296 are also of interest in this regard.
There have been numerous kinetic studies reported in the literature for the reaction of hydroxylamine with monomeric amides such as acetamide, formamide, and acetanilide (W. P. Jencks and Mary Gilchrist, J. Am. Chem. Soc., 86, 5616 (1964); S. O. Eriksson and B. Ariander-ohlson, Acta Chem. Scand., 26, 2759 (1972); and G. B. Sergeev, V. A. Batyuk, and B. M. Sergeev, Kinetika i Kataliz, 15, 236 (1974)). In all cases the optimum pH for this reaction was shown to be between 6 and 7. Jencks and Gilchrist mention a higher rate constant for the reaction above pH 9. These kinetic studies were generally conducted under dilute conditions with a large excess of hydroxylamine to give pseudo-first-order kinetics. Jencks and Gilchrist also state that the reaction is catalyzed by buffers such as imidazole, pyridine, acetate, and carbonate. F. Bergmann (Anal. Chem., 24, 1367 (1952)) has used the high pH reaction of hydroxylamine with amides as an analytical method for the determination of amides.
A. Meister et al (J. Boil. Chem. 215, 441 (1955)) also shows maximum hydroxamic acid formation at pH .about.6 for a variety of natural amides.
The above articles, which deal primarily with monomeric species undergoing hydroxamation, refer primarily to pseudo first-order kinetics. When monomeric species are reacted with hydroxylamine salts, the reaction is conducted at a very high hydroxylamine concentration and thus, the kinetics involved are very different and do not readily equate with the kinetics of a polymer system during the hydroxamation of which the hydroxylamine concentration is a minority. At high hydroxylamine concentrations, the rate of reaction will always be very fast. As the concentration of the hydroxylamine decreases, the reaction rate decreases proportionally and the efficiency of conversion of hydroxylamine into hydroxamate group also diminishes. Thus, at low concentrations of hydroxylamine as are experienced in polymer hydroxamation, particularly with high molecular weight polymers, the reaction rate and efficiency of hydroxylamine utilization are critical to the commercial success of the process. If a process could be developed wherein the reaction rate and efficiency of utilization of hydroxylamine was also increased, a long felt need in the art would be satisfied.